9 replies to this topic

[Andy69]

Not sure what's going on, but I've gotten a lot slower in the last year, relative to other drivers.  I'm not beating people I used to beat handily.  Some of that can be attributed to others improving, but I've also been losing ground against drivers who are already top 3 nationals finishers.  It's very frustrating.  I've been putting my grey matter to work trying to figure it out.

 

For background, the car:

 

87 CRX Si, former IT car, now autocross.  27.5 mm bars up front with stock ARB, GC coilovers in the back with a 3/4" ARB and 500 lb springs.  Illumina dampers all around.  At the beginning of this year it had 255 A7s on 13x9 spun steel wheels.  Now it has 235 Ecsta V700s on 13x9 Keizers.  The V700s were on the wheels when I got them, I have no idea how old they are.

 

It started this year.  At first I attributed it to the A7s being a season old and having sat the winter, but I'm not so sure.  I've had other R comp tires and I didn't experience the same drop off.  Could be something odd to Hoosiers.

 

The steel wheels were heavy, so I replaced them with a set of Keizers with the Ecsta tires.  They are definitely less grippy than even worn Hoosiers, but I've done well even with worse tires.

 

The same time I changed the wheels, I removed a lot of weight (175 lbs)  from the car. This included the roll cage.  It was 125 lbs by itself and it was a fair amount of weight up high, so it definitely changed the center of gravity.  I'm sure it was also making the car a lot stiffer, so maybe this is a factor.

 

The car definitely handled differently.  It was less tail happy, actually tending to push a bit where the back end used to come around.  It felt faster, turn in was better, it seemed to corner better according to my butt dyno, but it was ultimately slower overall.  Today we were in Blytheville, and the car was VERY tail happy - completely different than before.  I've noticed that before on that surface with this car.  It was cool - 60 degrees, so I had some trouble getting heat in the tires, but I was ultimately able to turn in an OK time, but I didn't even make the top ten in a 24 car field.  Very unusual for me.

 

The tires definitely don't help, but they aren't totally worthless.  I'm revisiting the removal of the roll cage as potentially causing the car to be slower due to loss of stiffness.  I did not add anything back, like strut bars.  It needs those, I think, but perhaps it needs some other suspension tweaking to match the new lower weight? (estimated to be around 1750 - I knew what the car weighed before  and I weighed every piece I took off).  I'm kind of at a loss here.

[cbstdscott]

If the back end is "loose" you need more roll stiffness in front.

 

Chassis stiffness is an issue with these cars. A front strut bar, a B pillar brace and a C pillar brace all contribute to making the car stiffer. A rear strut brace is less neccesary, that is the stiffest part of the car.

 

Scott

[Andy69]

It only does that at Blytheville - I noticed that the first time I was there when I had a completely different suspension and tire setup.  Last spring it didn't do it, but then I was running 255 Hoosier A7s.  Everywhere else the car is more neutral.  I suspect it has something to do with this weird fungus or something that seems to grow on the concrete there, although the faster folks seem to know how to handle it.  They have national events there so it's obviously not a huge problem.  There is probably some setup magic I need to do to make the car more neutral just at Blytheville.

 

SCCA rules allow me to add a two point strut bar to the front and rear.  I have a two point bar but I had to take it off to install the camber plates.  At the time, the camber plates gave me a bigger advantage than the bar because of the roll cage.  I think removing the plates to put the bar back on would be a sideways move at best, so I think my options there are to find a bar that will fit with camber plates, or use the bottom end of the suspension to adjust camber (SCCA Rules allow either the top or the bottom but not both).  Using camber plates is the easier of the two.

 

I found those fender braces that Chedda is selling, but I don't think the rules allow those.

[cbstdscott]

Horses for courses. If you have a loose rear end at on one course, dial in some more front roll stiffness for that course only.

Definitely find a strut bar that works with the camber plates, I went back to a camber only plate set that works with my strut bar. It is that important.

A roll cage was ok but a B pillar brace is not? The pillar braces are a chassis mod, not a suspension mod.

No discussion about your rear suspension. What are you using?
The National Champion is using a HF axle. I threw away the internal torsion bar from my '87 Si.

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[Andy69]

Horses for courses. If you have a loose rear end at on one course, dial in some more front roll stiffness for that course only.

Definitely find a strut bar that works with the camber plates, I went back to a camber only plate set that works with my strut bar. It is that important.

A roll cage was ok but a B pillar brace is not? The pillar braces are a chassis mod, not a suspension mod.

No discussion about your rear suspension. What are you using?
The National Champion is using a HF axle. I threw away the internal torsion bar from my '87 Si.

Sent from my SM-G920V using Tapatalk

 

If it's not specifically mentioned as allowed, it's not allowed, so a B-pillar brace is out.

 

One thing I noticed the first time the rear of my car went crazy at Blytheville was turning the front struts DOWN a couple of clicks didn't fix the problem entirely but it did calm it down considerably.  

 

That seems counterintuitive, since to reduce oversteer you stiffen the front, not soften it.  But on the Tokicos, the knob adjusts rebound - compression is not adjustable.  The only thing I can think of is perhaps the rebound on the inner side of the car, being stiffer relative to the outside of the car, is slowing the weight transfer slightly and giving the outside rear wheel time to start sliding.

 

I had hesitated to use the rear axle set up on my car as I questioned it durability, but if people are using it, they're using it.

[Andy69]

Some midnight thinking

 

I probably need to check the car over for binding, particularly in the rear of the car.  Not sure how to do that, though.

 

I've noticed in pictures that I get quite a bit of roll in the front, but not in the rear - it just lifts up the inside wheel.

[cbstdscott]

A fresh set of bushings for the trailing arms will help to release binding. Chedda makes a set of replacement spherical bushings that are even better than the stock rubber bits.

 

Front roll equals rear oversteer. More roll stiffness in front will go a long way toward solving that problem.

 

You mentioned that you are concerned about the durability of the HF rear axle. Really? Nobody has ever had that problem.

 

On my 87 Si, I have removed the rear axle torsion bar and all the linkage to the right rear trailing arm. This will allow a lot more rotation in your chassis (Yaw) that will need to be controlled by adding more front roll stiffness. To do this you will need adjustable struts that actually do something. Time to upgrade to Teins or even better, Konis.

 

My reading of the rule book is that if the book does not mention it... it is allowed. I look for wording that specifically forbids something.

[Andy69]

A fresh set of bushings for the trailing arms will help to release binding. Chedda makes a set of replacement spherical bushings that are even better than the stock rubber bits.

 

Front roll equals rear oversteer. More roll stiffness in front will go a long way toward solving that problem.

 

You mentioned that you are concerned about the durability of the HF rear axle. Really? Nobody has ever had that problem.

 

On my 87 Si, I have removed the rear axle torsion bar and all the linkage to the right rear trailing arm. This will allow a lot more rotation in your chassis (Yaw) that will need to be controlled by adding more front roll stiffness. To do this you will need adjustable struts that actually do something. Time to upgrade to Teins or even better, Konis.

 

My reading of the rule book is that if the book does not mention it... it is allowed. I look for wording that specifically forbids something.

 

That will get you into trouble in SCCA.  The rules say if it's not specifically mentioned as allowed, it's not allowed.

 

Spherical bushings are not allowed, although they would be nice.  They can, however, be a better material than stock.

 

My concern about the rear axle comes from my experience with the front hub on the Si being prone to breakage, making the smaller HF hub probably unusable.  I assumed the rear was equally frail, but it seems that assumption was not correct.

 

Teins, or even Konis (unless I get a good deal somewhere) aren't in the cards at the moment.  Too many other upcoming expenses.

 

I have the bushings for the rear, just need to install them.  I'll see what that does.

[rallyxcrx]

Old tires are about 2 seconds slower than new ones, and if you don't keep your driving sharp, about one second there. Then theres about 1000 things that will make you go faster, suspension, alignment , engine, reduce weight, areo, etc. Nobody said car racing was cheap, I knocked out my automatic transmission in my stock 05 camry last weekend running 2 rallyxs and one autocross. A first and a third rallyxing, and emberrested most of the drivers at the autox, but about a 3500.00 set back, Dave     

[Andy69]

I think the biggest thing is all the weight I removed has affected how the car handles - particularly the roll cage, since I also lost the stiffness in addition to the weight.